This invention relates to controlling the flow of data among the nodes of a data communication network.
Two data terminals connected respectively to two different nodes of such a network communicate, in one typical scheme, via a so-called virtual circuit data path that passes through the two nodes and via a chain of intervening nodes and physical links that together complete the connection between the two data terminals. Each node or link may handle a large number of paths. The paths are multiplexed on the link. Each node has buffers that temporarily store inbound data of various paths until it can either be sent out along the outbound links of the respective paths or delivered to data terminals served by that node. The average rate at which inbound data is received cannot exceed the rate of outbound data for very long without the buffers overflowing and data being lost.
One technique for controlling the flow of data in such a network is called an ARQ window. In such a scheme a node receiving data over a path from an upstream node must periodically acknowledge receipt of blocks of data before the upstream node will send more. A maximum number of unacknowledged frames (the ARQ window) can be on the path at one time. The receiving node can thus regulate the quantity of data received over a given path by acknowledging or not acknowledging incoming frames.